Experiments are proposed to study the control of immunoglobulin gene expression in transgenic mice. In collaboration with Dr. Ralph Brinster, University of Pensylvania, cloned immunoglobulin genes will be microinjected into fertilized mouse eggs and the microinjected embryos will be developed to term in foster mothers. The following problems will be addressed in such transgenic mice and their offspring: 1) Allelic exclusion: Does the presence of microinjected, rearranged, functional Kappa, Lambda, or H immunoglobulin genes prevent the rearrangement and/or expression of endogenous immunoglobulin genes in developed B lymphocytes? 2) Regulation of antibody synthesis in transgenic mice which carry a microinjected Kappa and H chain gene whose products together bind a known antigen: How is the expression regulated by antigen when the genes are not under the influence of normal cis-acting mechanisms? Is the response of endogenous antibody genes influenced by antigen binding to the microinjected gene's H and L chains? 3) Mutation of V genes: will microinjected variable genes inserted at an abnormal chromosome location become mutated and if so, what sequences besides the target are required for mutation. 4) Sequences responsible for tissue specific expression of immunoglobulin genes: What are the target sequences around a microinjected immunoglobulin gene which respond to signals present in B cells, but not in other cells? 5) How does a microinjected immunoglobulin gene influence the expression of the flanking host genes. Preliminary published data of the P.I. and collaborators indicate that the experiments are feasible. All the essential methods of production of transgenic mice, molecular biology of DNA and RNA, immunochemistry and immunobiology are established in the laboratories of the P.I. and collaborators.